Catheter shaft having variable thickness layers and method of making

ABSTRACT

A catheter having a shaft with at least two variable layers, in which the relative proportions of the two layers changes along at least a part of the multilayered shaft section. The catheter shaft includes a cotapered transition section having a first layer tapering to a decreased thickness, and a second layer inversely tapering to an increased thickness. In one embodiment, the shaft has one or more tapered outer and/or inner surfaces in addition to the cotapered transition. The tapered outer or inner surface of the shaft is typically longitudinally displaced from the cotapered transition section. In a presently preferred embodiment, the shaft having a cotapered transition section is coextruded. Another aspect of the invention includes a method of making a shaft having a cotapered transition section. The shaft of the invention provides improved transitions between shaft sections, to thereby change characteristics such as the shaft stiffness along the length of the catheter.

BACKGROUND OF THE INVENTION

[0001] This invention generally relates to catheters, and particularlyintravascular catheters for use in percutaneous transluminal coronaryangioplasty (PTCA) or for the delivery of stents.

[0002] In a typical PTCA procedure, a dilatation balloon catheter isadvanced over a guidewire to a desired location within the patient'scoronary anatomy where the balloon of the dilatation catheter ispositioned within the stenosis to be dilated. The balloon is theninflated with radiopaque liquid at relatively high pressures (generally4-16 atmospheres) to dilate the stenosed region of the diseased artery.One or more inflations may be needed to effectively dilate the stenosis.

[0003] In such angioplasty procedures, there may be restenosis of theartery, i.e. reformation of the arterial blockage, which necessitateseither another angioplasty procedure, or some other method of repairingor strengthening the dilated area. To reduce the restenosis rate and tostrengthen the dilated area, physicians frequently implant anintravascular prosthesis, generally called a stent, inside the artery atthe site of the lesion. Stents are usually delivered to a desiredlocation within a coronary artery in a contracted condition on a balloonof a catheter which is similar in many respects to a balloon angioplastycatheter, and expanded to a larger diameter by expansion of the balloon.The balloon is deflated to remove the catheter and the stent left inplace within the artery at the site of the dilated lesion.

[0004] An essential step in effectively performing a PTCA procedure isproperly positioning the balloon catheter at a desired location withinthe coronary artery. To properly position the balloon at the stenosedregion, the catheter must have good pushability and flexibility, to bereadily advanceable within the tortuous anatomy of the patient'svasculature. Conventional catheter shafts may typically include multipleshaft sections having different flexibilities along the length of thecatheter to improve the maneuverability of the catheter. A variety ofmethods have been used to form shafts having sections with variableflexibility, including forming multilayered shafts having transitionsections in which a first layer tapers to a larger thickness as a secondlayer tapers inversely to a smaller thickness. One difficulty has beencontrolling the changes in the thickness of the first layer and secondlayer. Insufficient control, resulting in disadvantageously abrupt orgradual changes in the proportions of a first and second polymer, mayresult from conventional coextrusion systems, such as those using on/offvalves to control the flow of the polymers making up the two layers.U.S. Pat. No. 5,725,814 (Harris), incorporated by reference herein inits entirety, discloses a coextrusion apparatus having gear pumps at theoutput ends of multiple extruders. The gear pumps are used to vary therelative amount of the polymers extruded and to thus form an extrudedtube having multiple layers, the proportions of which vary along thelength of the extruded tube.

[0005] What has been needed is a catheter which is highly trackablewithin the patient's anatomy, with improved flexibility and pushability.

SUMMARY OF THE INVENTION

[0006] This invention is directed to a catheter having a shaft with atleast two variable layers, wherein the relative proportions of the twolayers change along at least a section of the multilayered shaft. Thecatheter shaft includes a section having a first layer tapering to adecreased thickness, and a second layer inversely tapering to anincreased thickness, referred to herein as a cotapered transitionsection. The term inversely tapering should be understood to mean thesecond layer tapers in an opposite direction to the taper of the firstlayer. In one embodiment, the shaft has one or more tapered outer and/orinner surfaces in addition to the cotapered transition. The taperedouter or inner surface section of the shaft is typically longitudinallydisplaced from the cotapered transition section and may be directlyadjacent to the cotapered transition section. In a presently preferredembodiment, the shaft having a cotapered transition section iscoextruded. Another aspect of the invention includes a method of makinga shaft having a cotapered transition section. The shaft of theinvention provides improved transitions between shaft sections, tothereby change characteristics such as the shaft stiffness along thelength of the catheter.

[0007] In one embodiment of the invention, the catheter shaft has afirst longitudinal section having a cotapered transition section with afirst layer having a tapered surface and a second layer having aninversely tapered surface, and a second longitudinal section with atapered outer diameter. One of the first or the second layers has atapered inner surface and a tapered outer surface in the secondlongitudinal section of the catheter shaft, and one of the first orsecond layers has a substantially constant wall thickness in the secondlongitudinal section of the catheter shaft. The first longitudinalsection may be proximal or distal to the second longitudinal section,and the first layer may be an inner layer or an outer layer relative tothe second layer.

[0008] In another embodiment of the invention, the catheter shaft has afirst longitudinal section having a cotapered transition section with afirst layer having a tapered surface and a second layer having aninversely tapered surface, and a second longitudinal section with atapered outer diameter and with the first layer having a substantiallyconstant wall thickness from at least a portion of the secondlongitudinal section to the distal end of the catheter shaft. In apresently preferred embodiment, the first longitudinal section isproximal to the second longitudinal section, and the first layer is aninner layer relative to the second layer.

[0009] In another embodiment, the catheter shaft has a firstlongitudinal section having a cotapered transition section with a firstlayer having a tapered surface and a second layer having an inverselytapered surface, and a second longitudinal section distal to anddirectly adjacent to the first longitudinal section, with a taperedouter diameter and with the first layer having an outer surface taperingdistally to a smaller outer diameter and the second layer having anouter surface tapering distally to a smaller outer diameter. The firstlongitudinal section may be proximal or distal to the secondlongitudinal section, and the first layer may be an inner layer or anouter layer relative to the second layer. The first and second layersmay be extend along the entire length of the shaft, or may have aproximal end and/or a distal end which terminate between the proximaland distal ends of the shaft.

[0010] In one embodiment, the catheter is a balloon catheter generallyincluding an elongated shaft having a cotapered transition section inaccordance with the invention and a balloon secured to a distal portionof the shaft.

[0011] A method of making an elongated multilayered catheter shafthaving at least a first layer and a second layer and having a cotaperedsection in which the first layer tapers from a larger wall thickness toa smaller wall thickness and the second layer inversely tapers from asmaller wall thickness to a larger wall thickness, includes extrudingthe first layer from an extruder having a first pump at an output endthereof, and extruding the second layer from a second extruder having asecond pump at an output end thereof. The first and second pumps arepreferably gear pumps. The first and second layers are preferablycoextruded through a coextrusion die downstream from the first andsecond extruders and first and second gear pumps. The direction of thefirst pump, e.g., the rotation of the first gear pump, is reversed to atleast in part form the tapered surface in the first layer, and the speedof the second pump is increased from a first speed to a second speed toform the inverse taper in the second layer. As a result of temporarilysetting the first gear pump into reverse rotation, plastic pressure isremoved from the layer being tapered, and the time required to taper thefirst layer from the larger to the smaller wall thickness isadvantageously reduced, to thereby produce a tailored, shortertransition. In one embodiment, forming the cotapered section includestemporarily speeding up the speed of the second gear pump from a firstspeed to a second speed which is greater than the steady state thirdspeed used to form a section of the shaft after the cotapered section,to thereby reduce the time required to taper the second layer from thesmaller wall thickness to the larger wall thickness. Thus, in oneembodiment, a section of the shaft, which is adjacent and distal to thecotapered section, is formed by decreasing the speed of the second gearpump from the second speed used to form the cotapered section to a thirdspeed greater than the first speed used to form a section of the shaftbefore the cotapered section and less than the second speed. The methodof the invention provides improved short transitions varying therelative proportions of the first and second layers. The tailored shorttransitions are particularly advantageous in distal sections of thecatheter shaft, to provide rapid changes in flexural modulus of theshaft for improved maneuverability of the catheter in the highlytortuous distal vascular anatomy.

[0012] Preferably, the polymer forming the first layer is different fromthe polymer forming the second layer. The polymer forming the innerlayer of the cotapered section may have a hardness greater than, lessthan or equal to the hardness of the outer layer. In one embodiment, theviscosity of the polymers used to form the first and second layers isselected to minimize back pressure between the gear pumps and the die,and more specifically to minimize stored pressure energy which leads tolong transitions.

[0013] The catheter shaft of the invention has excellent flexibility,pushability, and trackability due to the variable layers of the shafthaving improved tapered transitions. The tapered transitions provideimproved force transmission, cross, and flexibility in the distal end ofthe catheter, and tailoring of the catheter shaft characteristics, whileavoiding the increased profile and increased risk of kinking inconventional fusion or adhesion junctions used to secure separate shaftsections together. The catheter shaft of the invention avoidssignificant negative effects on inflation/deflation time caused bydisadvantageous decreases in the size of the shaft lumen(s) at bondedjunctions. Additionally, one embodiment of the invention involvesproviding a catheter shaft having a tailored, short transition,providing improved rapid changes in the shaft flexural modulus whileavoiding disadvantageously abrupt transitions. These and otheradvantages of the invention will become more apparent from the followingdetailed description when taken in conjunction with the accompanyingexemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is an elevational view, partially in section, of a ballooncatheter which embodies features of the invention.

[0015]FIG. 2 is an enlarged longitudinal cross sectional view of thecatheter shown in FIG. 1, taken within circle 2, illustrating a shaftsection having a proximal longitudinal section with cotapered inner andouter layers, and a distal longitudinal section with a tapered outerdiameter and the inner layer having a tapered inner surface and atapered outer surface and the outer layer having a substantiallyconstant wall thickness in the distal longitudinal direction.

[0016]FIG. 3 is a transverse cross-section of the catheter shaft sectionshown in FIG. 2, taken along line 3-3.

[0017]FIG. 4 is an enlarged longitudinal cross sectional view of anotherembodiment of a catheter shaft which embodies features of the invention,illustrating a shaft section having a proximal longitudinal section withcotapered inner and outer layers, and a distal longitudinal section witha tapered outer diameter and the inner layer having a substantiallyconstant wall thickness in the distal longitudinal section and the outerlayer having a tapered inner surface and a tapered outer surface in thedistal longitudinal section.

[0018]FIG. 5 is an enlarged longitudinal cross sectional view of anotherembodiment of a catheter shaft which embodies features of the invention,illustrating a shaft section having a proximal longitudinal section witha tapered outer diameter and with an inner layer having a tapered innersurface and a tapered outer surface and the outer layer having asubstantially constant wall thickness in the proximal longitudinalsection, and a distal longitudinal shaft section with cotapered innerand outer layers.

[0019]FIG. 6 is an enlarged longitudinal cross sectional view of anotherembodiment of a catheter shaft which embodies features of the invention,illustrating a shaft section having a proximal longitudinal shaftsection with cotapered inner and outer layers, and a distal longitudinalshaft section with a tapered outer diameter, the first layer having asubstantially constant wall thickness from a location on the distallongitudinal section to the distal end of the multilayered shaft.

[0020]FIG. 7 is an enlarged longitudinal cross sectional view of anotherembodiment of a catheter shaft which embodies features of the invention,illustrating a shaft section having cotapered inner and outer layers,the inner layer having a distal end proximal to the distal end of theouter layer, and the outer layer having a proximal end distal to theproximal end of the inner layer.

[0021]FIG. 8 is a schematic block diagram of a co-extrusion apparatususeful in extruding polymeric tubes according to a method which embodiesfeatures of the invention.

[0022]FIG. 9 is a graph of gear pump speed versus time useful inextruding polymeric tubes according to a method which embodies featuresof the invention, in which the first gear pump extruding the first layerbeing tapered from thick to thin is temporarily reversed.

[0023]FIG. 10 is a graph of gear pump speed versus time useful inextruding polymeric tubes according to a method which embodies featuresof the invention, in which the second gear pump extruding the secondlayer being tapered from thin to thick is, temporarily sped up beyondthe steady state operating speed of the pump used to form a section ofthe shaft after the cotapered section.

[0024]FIG. 11 is an enlarged longitudinal cross sectional view ofanother embodiment of a catheter shaft which embodies features of theinvention, having cotapered inner and outer layers formed according to amethod which embodies features of the invention.

[0025]FIG. 12 is an schematic block diagram of a co-extrusion apparatushaving an extended flow divider useful in extruding polymeric tubesaccording to a method which embodies features of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026]FIG. 1 illustrates an intraluminal catheter 10 which embodiesfeatures of the invention, generally comprising an elongated shaft 11having a proximal end 12 and a distal end 13. Catheter 10 is a ballooncatheter having a balloon 15 secured to a distal portion of the shaft11. In the embodiment illustrated in FIG. 1, the shaft 11 comprises anouter tubular member 16 defining in part an inflation lumen 17 (FIG. 2),and an inner tubular member 18 disposed within the outer tubular memberand defining a guidewire lumen 19 (FIG. 2) configured to slidablyreceive a guidewire 24. In the illustrated embodiment, the coaxialrelationship between outer tubular member 16 and inner tubular member 18defines annular inflation lumen 17. Balloon 15 has a proximal endsealingly secured to the distal end of outer tubular member 16 and adistal end sealingly secured to the distal end of inner tubular member18, so that its inflatable interior 21 is in fluid communication withinflation lumen 17. Adapter 22 at the proximal end of the shaft 11 isconfigured to direct inflation fluid through arm 23 into inflation lumen17, and provide access to guidewire lumen 19. In accordance with theinvention, at least a section of the catheter shaft 11 has sectionhereinafter referred to as a cotapered section with a first layer 26having a tapered surface and a second layer 27 having an inverselytapered surface. FIG. 2, illustrates an enlarged longitudinal crosssection of a distal portion of the catheter 10 shown in FIG. 1, takenalong lines 2-2. FIGS. 4-7 illustrate alternative embodiments of acatheter shaft which embodies features of the invention.

[0027] In the embodiment illustrated in FIG. 2, the shaft 11 has a firstlayer 26 which is an inner layer, and a second layer 27 which is anouter layer. The shaft section 30 of the shaft 11 illustrated in FIG. 2has a first longitudinal section 32, a second longitudinal section 34,and a third longitudinal section 36. In the embodiment illustrated inFIG. 2, the shaft section 30 is a section of the outer tubular member16. However, the shaft section 30 may be used in a variety of shaftdesigns including a section of inner tubular member 18, or a section ofan extruded single, dual or multilumen lumen shaft. FIG. 3 illustrates atransverse cross sectional view of the shaft 11 shown in FIG. 2, takenalong line 2-2. In the shaft first longitudinal section 32 the inner andouter layers 26/27 cotaper, so that the inner layer has a taperedsurface and the outer layer 27 has a surface tapering inversely thereto.The first longitudinal section 32 is proximal to second longitudinalsection. The second longitudinal section 34 has a tapered outerdiameter. Thus, in the embodiment illustrated in FIG. 2, the distal endof the first longitudinal section 32 is at the location on the shaftwhere the outer diameter of the shaft begins to taper. In the secondlongitudinal section 34, the inner layer 26 has a tapered inner surfaceand a tapered outer surface, and the outer layer 27 has a substantiallyconstant wall thickness. In the embodiment illustrated in FIG. 2, theshaft 11 includes third longitudinal section 36 distal to the secondlongitudinal section 34 with the inner layer 26 and outer layer 27cotapering. The third longitudinal section 36 has a substantiallyconstant outer diameter less than the outer diameter of the firstlongitudinal section 32.

[0028] In the embodiment illustrated in FIG. 4, the first longitudinalsection 32 of the catheter shaft, having cotapered first and secondlayers 26/27, is proximal to the second longitudinal section 34 having atapered outer diameter. The first layer 26 is an inner layer, and thesecond layer 27 is an outer layer. In the second longitudinal section34, the outer layer 27 has a tapered inner surface and a tapered outersurface, and the inner layer 26 has a substantially constant wallthickness. In the embodiment illustrated in FIG. 4, the shaft 11includes an intermediate shaft section 38 between and directly adjacentto the first and second longitudinal sections 32/34 of the cathetershaft, having a constant outer diameter. In the embodiment illustratedin FIG. 4, the inner surface of the outer layer 27 and the outer surfaceof the inner layer 26 are not tapered in the intermediate section 38, sothat the intermediate section 38 has a constant interfacial diameterbetween the inner and outer layers 26/27. It should be understood that,as discussed above in relation to the embodiment shown in FIG. 2, theshaft section 30 illustrated in FIG. 4 and in the remaining figures maybe used in a variety of shaft designs, as a section of an inner and/orouter tubular member, or a section of an extruded single, dual ormultilumen lumen shaft.

[0029] In the embodiment illustrated in FIG. 5, the first longitudinalsection 32, having cotapered first and second layers 26/27, is distal tothe second longitudinal section 34, having a tapered outer diameter. Thefirst Layer 26 is an inner layer, and the second layer 27 is an outerlayer. In the second longitudinal section 34, the inner layer 26 has atapered inner surface and a tapered outer surface, and the outer layer27 has a substantially constant wall thickness. In the embodimentillustrated in FIG. 5, the shaft 11 includes an intermediate section 40between the first longitudinal section 32 and the second longitudinalsection 34, with inner and outer layers 26/27 having a constantinterfacial diameter in the intermediate section 40.

[0030] Thus, in the embodiments illustrated in FIGS. 2, 4 and 5, thecatheter shaft 11 comprises a shaft section 30 having a firstlongitudinal section 32 with a first layer 26 having a tapered surface,and a second layer 27 having an inversely tapered surface, and a secondlongitudinal section 34 with a tapered outer diameter, one of the firstor the second layers 26/27 having a tapered inner surface and a taperedouter surface in the second longitudinal section 34, and one of thefirst or the second layers 26/27 having a substantially constant wallthickness in the second longitudinal section 34.

[0031] In an alternative embodiment of the invention illustrated in FIG.6, the shaft comprises a first longitudinal section 42 with cotaperedfirst and second layers 26/27, and a second longitudinal section 44 witha tapered outer diameter. In the embodiment illustrated in FIG. 6, thefirst longitudinal section 42 is proximal to the second longitudinalsection 44. The first layer 26 is an inner layer, and the second layer27 is an outer layer. In the second longitudinal section 44, the firstlayer 26 has a substantially constant wall thickness from at least aportion of the second longitudinal section preferably to an end of themultilayered shaft 11. In the embodiment illustrated in FIG. 6, thefirst longitudinal section 42 has a substantially constant outerdiameter. In the embodiment illustrated in FIG. 6, an intermediatesection 46 having a constant outer diameter and a constant interfacialdiameter between the inner and outer layers 26/27 is provided betweenfirst longitudinal section 42 and second longitudinal section 44, and aproximal tapered section 47 having a tapered outer diameter is providedproximal to the cotapered first longitudinal section 42.

[0032] In the embodiment illustrated in FIG. 6, an inner liner 48 on aninner surface of the first layer 26 defines the inner lumen of the shaft11 outer tubular member 16. Preferably, the inner liner 48 is alubricious material, such as HDPE or a fluoropolymer such as teflon.Although illustrated as an inner liner on an outer tubular member, theinner liner 48 may be provided on a shaft section defining a lumenconfigured for slidably receiving members such as guidewires, mandrels,and diagnostic or therapeutic instruments therein, to facilitateadvancement of such members therein. In the illustrated embodiment, theliner 48 has a substantially constant wall thickness.

[0033] In an alternative embodiment illustrated in FIG. 7, the shaftcomprises a first longitudinal section 52 with cotapered first layer 26and second layer 27, and a second longitudinal section 54 with a taperedouter diameter. In the embodiment illustrated in FIG. 7, the firstlongitudinal section 52 is proximal to the second longitudinal section54, and the first layer 26 is an inner layer and the second layer 27 isan outer layer. In the second longitudinal section 54, the inner layer26 and the outer layer 27 each have an outer surface tapering distallyto a smaller outer diameter. The shaft includes a third longitudinalsection 56 distal to the second longitudinal section 54, with the innerlayer 26 and outer layer 27 cotapering in the third longitudinal section56. The third longitudinal section 56 has a substantially constant outerdiameter less than the outer diameter of the first longitudinal section52. In the embodiment illustrated in FIG. 7, the first and second layers26/27 do not extend the length of the shaft 11, so that the distal endof the first layer 26 is proximal to the distal end of the second layer27, and the proximal end of the second layer 27 is distal to theproximal end of the first layer 26. Specifically, in the embodimentillustrated in FIG. 7, the distal end of the first layer 26 terminatesat the distal end of the cotapered third longitudinal section 56, andthe proximal end of the second layer 27 terminates at the proximal endof the cotapered first longitudinal section 52. In alternativeembodiments, the first and second layers are continuous, extending fromthe proximal to the distal end of the shaft 11.

[0034] The inner layer may be provided with an inner surface taperingdistally to a smaller inner diameter, such as the inner layer 26illustrated in FIGS. 2, 4, 5 and 7 having the inner layer taperingdistally in the second longitudinal section 34/54 of the shaft.Alternatively the inner layer 26 may have a substantially constant innerdiameter. The terminology substantially constant should be understood tomean that the diameter of the shaft or wall thickness of the individuallayer of the shaft is not intentionally tapered and is thereforeconstant within the tolerances of the method used to form the member.Thus, for an extruded shaft section, the substantially constant outerdiameter of an individual layer preferably varies by not more than about±0.001 inch, and the substantially constant wall thickness of anindividual layer preferably varies by not more than about ±0.0005 inch.

[0035] The first layer 26 and the second layer 27 may be formed of avariety of suitable polymeric materials depending on the configurationof the shaft and the desired use and characteristics of the shaft. In apresently preferred embodiment, the first and second layers 26/27 areformed of polymeric materials having different characteristics such asShore Durometer hardness, softness, and lubricity. In one embodiment,the polymeric material which is present in a larger relative proportionin the distal shaft section than in the proximal shaft section, such asthe outer layer in the embodiment of FIG. 2, is formed of a polymericmaterial having a lower Shore Durometer hardness than the polymericmaterial forming the other layer, to thus provide a relatively flexibledistal shaft section. Presently preferred polymeric materials used toform the outer layer in the embodiment of FIG. 2 include polyamides suchas nylon, polyamide block copolymers such as Pebax (polyether blockamide), polyethylene based adhesives such as PRIMACOR, polyolefins, lowdensity polyethylene (LDPE), high density polyethylene (HDPE),polyurethane, and polyesters such as HYTREL or ARNITEL. Presentlypreferred polymeric materials used to form the outer layer in theembodiment of FIG. 2 have a Shore durometer hardness of about 90A toabout 70D, preferably about 50D to about 60D. However, the choice ofmaterial depends on a variety of factors including the desiredapplication and the method used to make the shaft. In one presentlypreferred embodiment, the inner layer is a lubricious material, tofacilitate advancement of members such as guidewires therein. However, athin lubricious liner on an inner surface of the inner layer may be usedto provide the desired lubricity to the wall defining the inner lumen ofthe shaft. Presently preferred polymeric materials used to form theinner layer in the embodiment of FIG. 2 include polyamide blockcopolymers such as Pebax, polyurethanes, polyesters such as HYTREL orARNITEL, and polyolefins such as HDPE. Presently preferred polymericmaterials used to form the inner layer in the embodiment of FIG. 2 havea Shore durometer hardness of about 60D to about 82D. In one embodiment,the polymeric materials used to form the inner and outer layers arecompatible, and can be heat bonded together.

[0036]FIG. 8 illustrates an apparatus 60 useful in a method of making acotapered section which embodies features of the invention. Apparatus 60generally comprises at least two extruders 62, each extruder having apump 64, which in a presently preferred embodiment is a gear pump, at anoutput end of the extruder 62. A coextrusion cross-head 66 with acoextrusion cross-head die is at the output end of each gear pump 64.Additional extruders 62 and corresponding gear pumps 64 can be providedif a catheter shaft having more than two coextruded cotapered layers aredesired. A control system (not shown) is provided to control theextruders and pumps. The gear pumps are used to vary the relative amountof the polymers extruded to form a cotapered section. In one embodimentof the invention, a gear pump 64 is temporarily set into reverserotation to form the cotapered layer tapering from a larger wallthickness to a smaller wall thickness. In another embodiment, a gearpump 64 is temporarily sped up beyond the steady state operating speedof the gear pump to form the cotapered layer tapering from a smallerwall thickness to a larger wall thickness. A method of making anelongated multilayered catheter shaft, generally comprises extruding afirst layer from an extruder having a first gear pump at an output endthereof, and coextruding a second layer with the first layer from asecond extruder having a second gear pump at an output end thereof. FIG.11 illustrates an elongated shaft 70 formed according to a method of theinvention, having a first layer 26, a second layer 27, a cotaperedsection 71, a proximal section 72 and a distal section 73. Cotaperedsection 71 of the shaft is formed by reversing the rotation of the firstgear pump 64 to at least in part form the taper in the first layer 26tapering from a greater wall thickness to a smaller wall thickness.Thus, the speed of the first gear pump 64 in the forward direction isreduced to zero and then the speed in the reverse direction is increasedto a value greater than zero. The speed setting of the first gear pump64 in the reverse direction may be less than, equal to, or greater thanthe speed setting of the first gear pump in the forward direction. Theouter or inner tapered surfaces of the shaft, such as the tapered outersurface of the outer layer 27 in the second longitudinal section 34 inthe embodiment of FIG. 2 can be formed using conventional taperingmethodology such as increasing the speed of the puller (not shown) whichdraws or elongates the extrudate exiting the die 66.

[0037] Conventional details regarding the configuration of theco-extrusion apparatus 60 used in the method of the invention, includingthe functioning of the extruders and the relative operation of theapparatus components can be found in U.S. Pat. No. 5,725,814, previouslyincorporated by reference.

[0038] The thickness of the first layer 26 and the second layer 27 inthe proximal shaft section 72 and the distal shaft section 73 willdepend on the materials used to form the shaft and the desired use andcharacteristics of the shaft. In one embodiment, the hardness of thepolymer forming first layer 26 (the inner layer in FIG. 11) is greaterthan the hardness of the polymer forming the second layer 27 (the outerlayer in FIG. 11), which in the embodiment illustrated in FIG. 11provides a relatively more flexible distal shaft section and arelatively less flexible proximal shaft section. However, in alternativeembodiments the first layer 26 may be formed of a polymeric materialhaving a hardness less than the hardness of the second layer polymericmaterial. Additionally, reinforcements, such as braided or wound metalor polymer members may be provided in one or more sections of one ormore of the layers.

[0039]FIG. 9 is a graph of the gear pump 64 speed versus time, useful ina method which embodies features of the invention in which the firstgear pump 64 is temporarily reversed to extrude the first layer 26 beingtapered from thick to thin in the cotapered section. For illustrationpurposes, the method will be discussed in terms of the embodiment of thecatheter shaft illustrated in FIG. 11 where catheter shaft 70 has atleast first layer 26 (hereafter the inner layer) and second layer 27(hereafter the outer layer) and a co-tapered section 71 in which theinner layer tapers distally to a smaller wall thickness and the outerlayer tapers inversely to the taper of the first layer, although themethod can be used to form a variety of shaft designs embodying featuresof the invention. The inner layer comprises a first polymer formed of,for example, nylon, HDPE, or HYTREL, having a Shore durometer hardnessof about 60D to about 82D, and the outer layer comprises a secondpolymer formed of, for example, Pebax, LDPE, or HYTREL, having a Shoredurometer hardness of about 55D to about 63D. In one embodiment, theinner and outer layers are compatible materials, so that the outer layeris Pebax when the inner layer is nylon, or LDPE when the inner layer isHDPE, or HYTREL when the inner layer is HYTREL. The proximal shaftsection 72 is made by extruding first polymer from the first extruder 62at a temperature between about 300° F. to about 600° F. with the firstgear pump in the forward direction at a speed of about 2 rpm to about 60rpm, preferably about 5 rpm to about 7 rpm, for about 0.5 seconds toabout 20 seconds, preferably about 1 second to about 3 seconds, and atthe same time coextruding second polymer from the second extruder 62 ata temperature between about 300° F. to about 600° F. with the secondgear pump in the forward direction at a speed of about 0.25 rpm to about10 rpm, preferably about 0.25 rpm to about 0.75 rpm, for about 0.5seconds to about 20 seconds, preferably about 1 second to about 3seconds, to form inner and outer layers 26/27, respectively, in theproximal section 72 of the shaft. The gear pump may be set to a speed ofabout 0 rpm to taper the layer to a zero thickness, or to merelydecrease the thickness of the layer without tapering to a zero thicknesswhen the extruded material does not quickly reflect the zero rpm pumpsetting. To form the cotapered section 71 of the shaft, the rotation ofthe first gear pump 64 is reversed, so that the first gear pump rampsdown to a negative speed setting of about −1 rpm to about −10 rpm inabout 0.1 seconds to about 2 seconds (i.e., ramps down at a rate ofabout 100 rpm/seconds) to form the taper in the inner layer 26 of thecotapered section 71, and the second gear pump ramps up to a speed ofabout 2 rpm to about 60 rpm, preferably about 2 rpm to about 20 rpm, inabout 0.1 seconds to about 2 seconds, preferably about 0.1 seconds toabout 0.2 seconds to form the taper in the outer layer 26 of thecotapered section 71. The first gear pump is typically held at thenegative speed setting for about 0.25 seconds to about 1 second, beforebeing set in a forward rotation of about 0 rpm to about 10 rpm,preferably about 0.25 to about 0.75 rpm, to form the inner layer 26 ofthe distal shaft section 73.

[0040] In the embodiment illustrated in FIG. 9, the speed of the secondgear pump 64 is increased to a speed setting of about 2 rpm to about 60rpm, in about 0.1 seconds to about 2 seconds, to form the outer layer inthe cotapered section 71, and the outer layer 27 of the distal shaftsection 73 is formed once the second gear pump reaches that increasedsteady state speed setting. In an alternative embodiment shown in FIG.10, illustrating a graph of the gear pump speed versus time, the speedof the second gear pump is temporarily set to a greater speed of about10 to about 100 rpm for about 0.25 seconds to about 1 second to form theouter layer of the cotapered section 71, and thereafter decreased to thesteady state speed of about 2 rpm to about 60 rpm, preferably about 5rpm to about 7 rpm, to form the outer layer of the distal shaft section73. The proximal shaft section inner layer 26 has a thickness of about0.0025 inch to about 0.004 inch, and the proximal shaft section outerlayer 27 has a thickness of about 0.0005 inch or about 0.001 inch toabout 0.002 inch. The distal shaft section inner layer 26 has athickness of about 0.0025 inch to about 0.004 inch, and the distal shaftsection outer layer 27 has a thickness of about 0.0005 inch or about0.001 inch to about 0.002 inch. The length of the cotapered section 71is about 5 inch to about 30 inch (13 cm to about 76 cm), and morespecifically about 10 inch to about 15 inch (25 cm to about 38 cm), andpreferably about 5 inch to about 10 inch. The length of the distal shaftsection is typically about 12 inch to about 15 inch, and the length ofthe proximal shaft section is typically about 40 inch to about 45 inch.Upon exiting from the extrusion die 66, the extrudate 70 is typicallyquenched in a water bath, and may be further processed by conventionalextrusion processing methods.

[0041] In one embodiment, the viscosity of the polymers used to form thefirst and second layers 26/27 is selected to minimize back pressurebetween the gear pumps 64 and the die 66. More specifically, the polymerforming the inner layer and the polymer forming the outer layer eachhave a relatively high melt flow index. Consequently, in one embodiment,shorter cotapered sections 71 are formed due to the decreased timerequired to release molten polymer compressed energy following changesin the gear pump settings during extrusion of the cotapered section. Ina presently preferred embodiment, the inner layer polymer has a meltflow index of about 10 to about 20 grams/10 minutes, and preferablyabout 12 grams/10 minutes, and the outer layer polymer has a melt flowindex of about 10 to about 20 grams/10 minutes, and preferably about 12grams/10 minutes. The melt flow index of the polymer forming the innerlayer may equal to or different from the melt flow index of the polymerforming the outer layer. As a consequence of the relatively high meltflow index of about 10 to about 20 grams/10 minutes, the polymer has arelatively low melt viscosity. The melt flow index is an inherentproperty of the polymer material which depends upon characteristics suchas the molecular weight of the material. Exemplary polymeric materialshaving a melt flow index of about 10 to about 20 grams/10 minutesinclude polyolefins.

[0042] In one embodiment, the extrusion apparatus is provided with anextended flow divider. FIG. 12 illustrates extended flow divider 80,which separates the flow of the first polymer 81 from the second polymer82 upstream of the die 83, and which extends closer toward the die exitthan does a standard flow divider. In the illustrated embodiment, theextended flow divider 80 extends to the end of the tapered section ofthe tip 84, in contrast to a standard flow divider which extends only tothe interface between the uniform diameter section of the tip 84 and thetapered section of the tip 84. Thus, the extended flow divider 80reduces the amount of the second polymer 82 present where the twopolymers 81/82 meet upstream of the die 83, such that the first polymer81 displaces the second polymer 82 faster than with a standard flowdivider, to thereby provide shorter cotapered transition lengths. Theextended flow divider reduced the transition length by about 50% andspecifically to about 10 inches to about 15 inches, increased the totallayer thickness change by about 15%, and increased the transition rateby about 80% in a cotapered transition, compared with a cotaperedtransition formed using a standard flow divider.

[0043] The dimensions of catheter 10 are determined largely by the sizeof the guidewires to be employed and the size of the artery or otherbody lumen through which the catheter must pass or the size of the stentbeing delivered. Typically, the outer tubular member 16 has anouter-diameter of about 0.02 to about 0.04 inch (0.05 to 0.10 cm),usually about 0.037 inch (0.094 cm), an inner diameter of about 0.015 toabout 0.035 inch (0.038 to 0.089 cm), usually about 0.03 inch (0.076cm). The wall thickness of the outer tubular member 16 can vary fromabout 0.002 to about 0.008 inch (0.0051 to 0.0201 cm), typically about0.003 inch (0.0076 cm). The inner tubular member 18 typically has anouter diameter of about 0.019 to about 0.028 inch, usually about 0.021inch. The overall working length of the catheter 10 may range from about100 to about 150 cm, and is typically about 147 cm. Preferably, balloon15 may have a length about 0.5 cm to about 4 cm and typically about 2 cmwith an inflated working diameter of about 1 to about 8 mm, and forcoronary applications about 1.5 mm to about 5 mm.

[0044] To the extent not discussed herein, the various cathetercomponents can be formed of conventional materials. Inner tubular member18 and outer tubular member 16 can be formed from materials alreadyfound useful in intravascular catheters such a polyethylene, polyvinylchloride, polyesters, polyamides, polyimides and composite materials.The various components may be joined by heat bonding or use ofadhesives.

[0045] The catheter shaft having at least first and second cotaperedlayers in accordance with the invention may be provided with additionallayers on an inner or an outer surface of the shaft, such as alubricious inner liner, one or more outer stiffening layers,reinforcement layers, and the like, coextruded with the first and secondlayers or separately applied thereto.

[0046] A variety of suitable catheter designs may be used, includingrapid exchange, over-the-wire, and fixed wire catheter designs. A rapidexchange catheter generally includes an inflation lumen extending fromthe proximal end of the catheter shaft to a location spaced proximal tothe distal end of the catheter shaft, a distal guidewire port in thedistal end of the catheter shaft, a proximal guidewire port spaceddistal to the proximal end of the catheter shaft, and a guidewire lumenextending between the proximal and distal guidewire ports. Typically,the proximal guidewire port is spaced a substantial distance from theproximal end of the catheter shaft and a relatively short distance fromthe distal guidewire port, so that the proximal guidewire port is closerto the distal guidewire port than to the proximal end of the cathetershaft.

[0047] Although not illustrated, the balloon catheter of the inventionmay be used to deliver prostheses, such as expandable stents, grafts,and the like, to a desired location within the patient's vasculature. Astent (not shown) comprising an expandable tubular body, typicallyhaving an open-walled structure, may be mounted on balloon 15, andballoon 15 may be inflated to expand the stent and seat it in thevessel. Additionally, catheter 10 may be used to touch up a previouslyimplanted stent by positioning balloon within stent lumen and expandingthe balloon to further expand the stent within a body lumen.

[0048] While the present invention is described herein in terms ofcertain preferred embodiments, those skilled in the art will recognizethat various modifications and improvements may be made to the inventionwithout departing from the scope thereof. For example, althoughintermediate shaft sections 38/40 are illustrated between the firstlongitudinal section 32 and the second longitudinal section 34 in someembodiments but not in others, it should be understood that suchintermediate sections may be provided or omitted on any of theembodiments. Although the tapered sections are illustrated as straight,linear tapers, the tapers may have a variety of suitable shapesincluding hyperbolic, curved shapes, by controlling extrusion conditionssuch as the speed of the gear pumps over time over the length of theprofile. Additionally, although discussed primarily in terms of acatheter shaft, it should be understood that the invention can be usedfor a variety of polymeric tubular members used as catheter componentssuch as sheaths, balloon tubes, and the like. Moreover, althoughindividual features of one embodiment of the invention may be discussedherein or shown in the drawings of the one embodiment and not in otherembodiments, it should be apparent that individual features of oneembodiment may be combined with one or more features of anotherembodiment or features from a plurality of embodiments.

What is claimed is:
 1. An intraluminal catheter, comprising an elongatedshaft having a proximal end, a distal end, at least one lumen, a firstlayer, a second layer, and having a) a first longitudinal section withthe first layer having a tapered surface, and the second layer having aninversely tapered surface; and b) a second longitudinal section with atapered outer diameter, at least one of the first or second layershaving a tapered inner surface and a tapered outer surface in the secondlongitudinal section, and at least one of the first or second layershaving a substantially constant wall thickness in the secondlongitudinal section.
 2. The catheter of claim 1 wherein the first andsecond layers are coextruded.
 3. The catheter of claim 1 wherein thefirst longitudinal section has a substantially constant outer diameter.4. The catheter of claim 1 wherein the first layer is an inner layerrelative to the second layer.
 5. The catheter of claim 4 wherein thefirst layer has a tapered inner surface and a tapered outer surface inthe second longitudinal section of the catheter shaft, and the secondlayer has a substantially constant wall thickness in the secondlongitudinal section of the catheter shaft.
 6. The catheter of claim 5wherein the first longitudinal section of the catheter shaft is proximalto the second longitudinal section of the catheter shaft.
 7. Thecatheter of claim 6 wherein the catheter shaft includes a thirdlongitudinal section distal to the second longitudinal section of thecatheter shaft, with a substantially constant outer diameter less thanthe outer diameter of the first longitudinal section of the cathetershaft, the first layer having a tapered surface, and the second layerhaving an inversely tapered surface.
 8. The catheter of claim 4 whereinthe first layer has a substantially constant wall thickness in thesecond longitudinal section of the catheter shaft, and the second layerhas a tapered inner surface and a tapered outer surface in the secondlongitudinal section of the catheter shaft.
 9. The catheter of claim 8including a shaft section between and directly adjacent to the first andsecond longitudinal sections of the catheter shaft, having a constantouter diameter and a constant interfacial diameter between the first andsecond layers.
 10. The catheter of claim 4 wherein the firstlongitudinal section of the catheter shaft is distal to the secondlongitudinal section of the catheter shaft, and the first layer has atapered inner surface and a tapered outer surface in the secondlongitudinal section of the catheter shaft, and the second layer has asubstantially constant wall thickness in the second longitudinal sectionof the catheter shaft.
 11. The catheter of claim 1 wherein the firstlayer tapers distally to a smaller wall thickness in the firstlongitudinal section of the catheter shaft, and the second layer tapersdistally to a smaller wall thickness in the second longitudinal sectionof the catheter shaft.
 12. The catheter of claim 1 wherein the first andsecond layers are continuous layers extending from the proximal end tothe distal end of the catheter shaft.
 13. The catheter of claim 1wherein the proximal end of the second layer is distal to the proximalend of the first layer, and the distal end of the first layer isproximal to the distal end of the second layer.
 14. The catheter ofclaim 1 wherein the catheter is a balloon catheter having a balloonsecured to at least a section of the catheter shaft with an interior influid communication with the shaft lumen.
 15. The catheter of claim 14wherein the shaft comprises an outer tubular member defining aninflation lumen in fluid communication with the balloon, and the shaftincludes an inner tubular member disposed within the inflation lumendefining a guidewire lumen, and wherein the balloon has a proximal endsealingly secured to a distal section of the outer tubular member and adistal end sealingly secured to a distal section of the inner tubularmember.
 16. The catheter of claim 1 wherein the first longitudinalsection of the shaft has a length of about 13 cm to about 76 cm.
 17. Thecatheter of claim 4 including an inner liner having a substantiallyconstant wall thickness on an inner surface of the first layer.
 18. Anintraluminal catheter, comprising an elongated shaft having a proximalend, a distal end, at least one lumen a first layer, a second layer, andhaving a) a proximal longitudinal section with the first layer having atapered surface, and the second layer having an inversely taperedsurface, the first layer being an inner layer relative to the secondlayer; and b) a distal longitudinal section with a tapered outerdiameter, the first layer having a substantially constant wall thicknessfrom at least a portion of the distal longitudinal section to the distalend of the shaft.
 19. The catheter of claim 18 wherein the proximallongitudinal section has a substantially constant outer diameter.
 20. Anintraluminal catheter, comprising an elongated shaft having a proximalend, a distal end, at least one lumen, a first layer, a second layer,and having a) a first longitudinal section with the first layer having atapered surface, and the second layer having an inversely taperedsurface; and b) a second longitudinal section distal to and directlyadjacent to the first longitudinal section, with a tapered outerdiameter, the first layer having an outer surface tapering distally to asmaller outer diameter in the second longitudinal section and the secondlayer having an outer surface tapering distally to a smaller outerdiameter in the second longitudinal section.
 21. The catheter of claim20 wherein the first longitudinal section has a substantially constantouter diameter.
 22. The catheter of claim 20 wherein the first layer hasan inner surface tapering distally to a smaller inner diameter.
 23. Anintraluminal catheter, comprising an elongated shaft having a proximalend, a distal end, at least one lumen, and having at least a sectionhaving cotapered first and second layers, so that the first layer has atapered surface and the second layer has an inversely tapered surface,the first layer being formed of a polymer having a melt flow index ofabout 10 to about 20 grams/minute, and the second layer being formed ofa polymer having a melt flow index of about 10 to about 20 grams/minute.24. The catheter of claim 23 wherein the first layer has a higher Shoredurometer hardness than the second layer and a melt flow index which isnot greater than the melt flow index of the second layer.
 25. A methodof making an elongated catheter shaft having at least a first and secondlayer, and a co-tapered section in which the first layer tapers to asmaller wall thickness and the second layer tapers inversely to thetaper of the first layer, comprising a) extruding the first layer froman extruder having a first gear pump at an output end thereof andco-extruding the second layer with the first layer from a secondextruder having a second gear pump at an output end thereof, and formingthe co-tapered section of the shaft by reversing the rotation of thefirst gear pump to at least in part form the taper in the first layer;and b) increasing the speed of the second gear pump from a first speedto a second speed to form the inverse taper in the second layer.
 26. Themethod of claim 25 including, after (ii), forming a distal section ofthe shaft adjacent to the co-tapered section by decreasing the speed ofthe second gear pump from the second speed to a third speed greater thanthe first speed of the second gear pump and less than the second speedof the second gear pump.
 27. The method of claim 25 wherein the shafthas a proximal section and distal section on either end of theco-tapered section having different relative proportions of the firstand second layers therein, and including forming the distal section bychanging the rotation of the first gear pump from the reversed rotationto a forward rotation and setting the speed of the first gear pump at asecond speed less than a first speed of the first gear pump used to formthe proximal section.
 28. The method of claim 27 wherein the co-taperedsection has a length of about 13 cm to about 25 cm, and forming thedistal section of the shaft includes decreasing the speed of the secondgear pump from the second speed to a third speed.
 29. The method ofclaim 27 wherein forming the co-tapered section of the shaft includesdecreasing a speed of the first gear pump from the first speed to athird speed.
 30. A method of making an elongated catheter shaft havingat east a first and second layer, and a section in which the first layertapers distally to a smaller wall thickness, comprising extruding thefirst layer from an extruder having a first gear pump at an output endthereof and co-extruding the second layer with the first layer from asecond extruder, and forming the section of the shaft by reversing therotation of the first gear pump to at least in part form the taper inthe first layer.